5-Lipoxygenase Inhibitor Zileuton Inhibits Neuronal Apoptosis Following Focal Cerebral Ischemia

Microglia-neuron-vascular interactions in ischemia

Cerebral ischemia is a devastating condition that results in impaired blood flow in the brain leading to acute brain injury. As the most common form of stroke, occlusion of cerebral arteries leads to a characteristic sequence of pathophysiological changes in the brain tissue. The mechanisms involved, and comorbidities that determine outcome after an ischemic event appear to be highly heterogeneous. On their own, the processes leading to neuronal injury in the absence of sufficient blood supply to meet the metabolic demand of the cells are complex and manifest at different temporal and spatial scales. While the contribution of non-neuronal cells to stroke pathophysiology is increasingly recognized, recent data show that microglia, the main immune cells of the central nervous system parenchyma, play previously unrecognized roles in basic physiological processes beyond their inflammatory functions, which markedly change during ischemic conditions. In this review, we aim to discuss some of the known microglia-neuron-vascular interactions assumed to contribute to the acute and delayed pathologies after cerebral ischemia. Because the mechanisms of neuronal injury have been extensively discussed in several excellent previous reviews, here we focus on some recently explored pathways that may directly or indirectly shape neuronal injury through microglia-related actions. These discoveries suggest that modulating gliovascular processes in different forms of stroke and other neurological disorders might have presently unexplored therapeutic potential in combination with neuroprotective and flow restoration strategies.

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

Identification of hub genes and pathways of ferroptosis in Fusarium keratitis by bioinformatics methods

Background

Fungal keratitis is a common blinding eye disease, and Fusarium is one of the main species that cause fungal keratitis. As is well known, oxidative stress plays an important role in Fusarium keratitis and it is also a significant initiating factor of ferroptosis. But the relationship between Fusarium keratitis and ferroptosis is currently unclear. This study aimed to speculate and validate potential ferroptosis-related genes in Fusarium keratitis using bioinformatics analysis, which provided ideas for further research on its specific mechanism and new targets for its treatment.

Methods

The microarray expression profiling dataset (GSE58291) came from Gene Expression Omnibus (GEO). The differentially expressed genes (DEGs) were obtained by the limma package of the R software. The DEGs were performed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Then, the DEGs were intersected with the genes in the ferroptosis database. The top 5 hub genes were obtained by the protein-protein interaction (PPI) network analysis and the cytoHubba plug-in of Cytoscape software. The hub genes were subjected to GSEA analysis. Then we analyzed the immune infiltration of the samples by CIBERSORT and ssGSEA algorithm. Finally, we validated the mRNA of hub genes by qPCR.

Results

A total of 1,368 DEGs were identified and 26 ferroptosis-related DEGs were obtained. At the same time, ferroptosis-related pathways were enriched by GO and KEGG using DEGs. HMOX1, CYBB, GPX2, ALOX5 and SRC were obtained by the PPI network analysis and the cytoHubba plug-in of Cytoscape software. The iron metabolism and immune response related pathways were enriched using GSEA. They included hematopoietic cell lineage, lysosome and FC gamma R mediated phagocytosis. T cells follicular helper, monocytes, macrophages and mast cells might play an important role in Fusarium keratitis using analysis of immune infiltration. Finally, qPCR confirmed that the expression of HMOX1, CYBB, ALOX5 mRNA in the DON group was significantly elevated, while the expression of GPX2 were significantly decreased.

Conclusions

Ferroptosis may play an important role in Fusarium keratitis. HMOX1, CYBB, ALOX5 and GPX2 may be key ferroptosis-related genes in the pathogenesis of Fusarium keratitis.

Plasma Lipid Mediators Associate With Clinical Outcome After Successful Endovascular Thrombectomy in Patients With Acute Ischemic Stroke

Background

Neuroinflammatory response contributes to early neurological deterioration (END) and unfavorable long-term functional outcome in patients with acute ischemic stroke (AIS) who recanalized successfully by endovascular thrombectomy (EVT), but there are no reliable biomarkers for their accurate prediction. Here, we sought to determine the temporal plasma profiles of the bioactive lipid mediators lipoxin A4 (LXA4), resolvin D1 (RvD1), and leukotriene B4 (LTB4) for their associations with clinical outcome.

Methods

We quantified levels of LXA4, RvD1, and LTB4 in blood samples retrospectively and longitudinally collected from consecutive AIS patients who underwent complete angiographic recanalization by EVT at admission (pre-EVT) and 24 hrs post-EVT. The primary outcome was unfavorable long-term functional outcome, defined as a 90-day modified Rankin Scale score of 3-6. Secondary outcome was END, defined as an increase in National Institutes of Health Stroke Scale (NIHSS) score ≥4 points at 24 hrs post-EVT.

Results

Eighty-one consecutive AIS patients and 20 healthy subjects were recruited for this study. Plasma levels of LXA4, RvD1, and LTB4 were significantly increased in post-EVT samples from AIS patients, as compared to those of healthy controls. END occurred in 17 (20.99%) patients, and 38 (46.91%) had unfavorable 90-day functional outcome. Multiple logistic regression analyses demonstrated that post-EVT levels of LXA4 (adjusted odd ratio [OR] 0.992, 95% confidence interval [CI] 0.987-0.998), ΔLXA4 (adjusted OR 0.995, 95% CI 0.991-0.999), LTB4 (adjusted OR 1.003, 95% CI 1.001-1.005), ΔLTB4 (adjusted OR 1.004, 95% CI 1.002-1.006), and post-EVT LXA4/LTB4 (adjusted OR 0.023, 95% CI 0.001-0.433) and RvD1/LTB4 (adjusted OR 0.196, 95% CI 0.057-0.682) ratios independently predicted END, and post-EVT LXA4 levels (adjusted OR 0.995, 95% CI 0.992-0.999), ΔLXA4 levels (adjusted OR 0.996, 95% CI 0.993-0.999), and post-EVT LXA4/LTB4 ratio (adjusted OR 0.285, 95% CI 0.096-0.845) independently predicted unfavorable 90-day functional outcome. These were validated using receiver operating characteristic curve analyses.

Conclusions

Plasma lipid mediators measured 24 hrs post-EVT were independent predictors for early and long-term outcomes. Further studies are needed to determine their causal-effect relationship, and whether the imbalance between anti-inflammatory/pro-resolving and pro-inflammatory lipid mediators could be a potential adjunct therapeutic target.

Recent Trends in the Management of Alzheimer's Disease: Current Therapeutic Options and Drug Repurposing Approaches

Alzheimer's disease is one of the most progressive forms of dementia, ultimately leading to death in aged populations. The major hallmarks of Alzheimer's disease include deposition of extracellular amyloid senile plaques and intracellular neurofibrillary tangles in brain neuronal cells. Although there are classical therapeutic options available for the treatment of the diseases, however, they provide only a symptomatic relief and do not modify the molecular pathophysiological course of the disease. Recent research advances in Alzheimer's disease have highlighted the potential role of anti-amyloid, anti-tau, and anti-inflammatory therapies. However, these therapies are still in different phases of pre-clinical/clinical development. In addition, drug repositioning/repurposing is another interesting and promising approach to explore rationalized options for the treatment of Alzheimer's disease. This review discusses the different aspects of the pathophysiological mechanism involved in the progression of Alzheimer's disease along with the limitations of current therapies. Furthermore, this review also highlights emerging investigational drugs along with recent drug repurposing approaches for Alzheimer's disease.

5-Lipoxygenase inhibition reduces inflammation and neuronal apoptosis via AKT signaling after subarachnoid hemorrhage in rats

Early brain injury (EBI) is a major contributor to the high mortality and morbidity after subarachnoid hemorrhage (SAH). Inflammatory responses and neuronal apoptosis are important causes of EBI. Because 5- lipoxygenase (5-LOX) is known to be involved various central nervous system diseases, we investigated the effects of 5-LOX inhibition during EBI after SAH. Zileuton and LY294002 were used to inhibit expression of 5-LOX and Akt, respectively. We found that 5-LOX expression was significantly increased in the cytoplasm of cortical neurons after SAH and was accompanied by upregulated expression of the inflammatory factors LTB4, TNF-α, IL-1β and IL-6; upregulation of the pro-apoptotic factor Bax; downregulation of the anti-apoptotic factor Bcl-2; and an increased apoptosis rate. Gastric Zileuton administration significantly suppressed all of those effects and improved neurological function. Zileuton also upregulated activated (phosphorylated) AKT levels, and these beneficial effects of Zileuton were abolished by intracerebroventricular infusion of the PI3K inhibitor LY294002. Taken together, these findings indicate that 5-LOX mediates pro-inflammatory and pro-apoptotic effects that contribute to EBI after SAH and that those effects are suppressed by activation of PI3K/Akt signaling. This suggests targeting 5-LOX may be an effective approach to treating EBI after SAH.

High ability of zileuton ((±)-1-(1-benzo[b]thien-2-ylethyl)-1-hydroxyurea) to stimulate IK(Ca) but suppress IK(DR) and IK(M) independently of 5-lipoxygenase inhibition

Zileuton (Zyflo®) is regarded to be an inhibitor of 5-lipoxygenase. Although its effect on Ca²⁺-activated K⁺ currents has been reported, its overall ionic effects on neurons are uncertain. In whole-cell current recordings, zileuton increased the amplitude of Ca²⁺-activated K⁺ currents with an EC₅₀ of 3.2 μM in pituitary GH₃ lactotrophs. Furthermore, zileuton decreased the amplitudes of both delayed-rectifier K⁺ current (I_K(DR)) and M-type K⁺ current (I_K(M)). Conversely, no modification of hyperpolarization-activated cation current (I_h) was demonstrated in its presence of zileuton, although the subsequent addition of cilobradine effectively suppressed the current. In inside-out current recordings, the addition of zileuton to the bath increased the probability of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels; however, the subsequent addition of GAL-021 effectively reversed the stimulation of channel activity. The kinetic analyses showed an evident shortening in the slow component of mean closed time of BK_Ca channels in the presence of zileuton, with minimal change in mean open time or that in the fast component of mean closed time. The elevation of BK_Ca channels caused by zileuton was also observed in hippocampal mHippoE-14 neurons, without any modification of single-channel amplitude. In conclusion, except for its suppression of 5-lipoxygenase, our results indicate that zileuton does not exclusively act on BK_Ca channels, and its inhibitory effects on I_K(DR) and I_K(M) may combine to exert strong influence on the functional activities of electrically excitable cells in vivo.

Lipids and Lipid Mediators Associated with the Risk and Pathology of Ischemic Stroke

Stroke is a severe neurological disorder in humans that results from an interruption of the blood supply to the brain. Worldwide, stoke affects over 100 million people each year and is the second largest contributor to disability. Dyslipidemia is a modifiable risk factor for stroke that is associated with an increased risk of the disease. Traditional and non-traditional lipid measures are proposed as biomarkers for the better detection of subclinical disease. In the central nervous system, lipids and lipid mediators are essential to sustain the normal brain tissue structure and function. Pathways leading to post-stroke brain deterioration include the metabolism of polyunsaturated fatty acids. A variety of lipid mediators are generated from fatty acids and these molecules may have either neuroprotective or neurodegenerative effects on the post-stroke brain tissue; therefore, they largely contribute to the outcome and recovery from stroke. In this review, we provide an overview of serum lipids associated with the risk of ischemic stroke. We also discuss the role of lipid mediators, with particular emphasis on eicosanoids, in the pathology of ischemic stroke. Finally, we summarize the latest research on potential targets in lipid metabolic pathways for ischemic stroke treatment and on the development of new stroke risk biomarkers for use in clinical practice.

Antagonism of cysteinyl leukotrienes and their receptors as a neuroinflammatory target in Alzheimer's disease

BACKGROUND

Alzheimer's disease is a complex multifaceted neurodegenerative disorder. It is characterized by the deposition of extracellular amyloid senile plaques and intracellular neurofibrillary tangles leading to progressive dementia and death in aged adult population. Recent emerging research has highlighted a potential pharmacological role of 5-lipoxyenase-cysteinyl leukotriene pathway in molecular pathogenesis of Alzheimer's disease.

OBJECTIVE

Although cysteinyl leukotrienes and their receptors have a major clinical role in chronic respiratory inflammation, their roles in chronic neuroinflammation in Alzheimer's disease need a detailed and careful exploration.

RESULTS AND CONCLUSION

This review article highlights a novel role of cysteinyl leukotrienes and their receptors in pathophysiology of Alzheimer's disease in order to understand the underlying molecular mechanism. In addition, it summarizes the recent advances in various pre-clinical and clinical strategies used to modulate this pathway for therapeutic targeting of Alzheimer's disease.

Lipid mediators and sterile inflammation in ischemic stroke

Stroke is one of the major causes of lethality and disability, yet few effective therapies have been established for ischemic stroke. Inflammation in the ischemic brain is induced by the infiltration and subsequent activation of immune cells. Loss of cerebral blood flow and ischemic brain-cell death trigger the activation of infiltrating immune cells and drastic changes in the lipid content of the ischemic brain. In particular, polyunsaturated fatty acids and their metabolites regulate cerebral post-ischemic inflammation and ischemic stroke pathologies. In this review, we discuss the relationships between the lipid mediators and cerebral post-ischemic inflammation and their relevance to possible future therapeutic strategies targeting lipid mediators for ischemic stroke.

Early and Sustained Increases in Leukotriene B4 Levels Are Associated with Poor Clinical Outcome in Ischemic Stroke Patients

Leukotriene B4 (LTB4) has been implicated in ischemic stroke pathology. We examined the prognostic significance of LTB4 levels in patients with acute middle cerebral artery (MCA) infarction and their mechanisms in rat stroke models. In ischemic stroke patients with middle cerebral artery infarction, plasma LTB4 levels were found to increase rapidly, roughly doubling within 24 h when compared to initial post-stroke levels. Further analyses indicate that poor functional recovery is associated with early and more sustained increase in LTB4 rather than the peak levels. Results from studies using a rat embolic stroke model showed increased 5-lipoxygenase (5-LOX) expression in the ipsilateral infarcted cortex compared with sham control or respective contralateral regions at 24 h post-stroke with a concomitant increase in LTB4 levels. In addition, neutrophil influx was also observed in the infarcted cortex. Double immunostaining indicated that neutrophils express 5-LOX and leukotriene A4 hydrolase (LTA4H), highlighting the pivotal contributions of neutrophils as a source of LTB4. Importantly, rise in plasma LTB4 levels corresponded with an increase in LTB4 amount in the infarcted cortex, thereby supporting the use of plasma as a surrogate for brain LTB4 levels. Pre-stroke LTB4 loading increased brain infarct volume in tMCAO rats. Conversely, administration of the 5-LOX-activating protein (FLAP) inhibitor BAY-X1005 or B-leukotriene receptor (BLTR) antagonist LY255283 decreased the infarct volume by a similar extent. To conclude, targeted interruption of the LTB4 pathway might be a viable treatment strategy for acute ischemic stroke.

Zileuton ameliorates depressive-like behaviors, hippocampal neuroinflammation, apoptosis and synapse dysfunction in mice exposed to chronic mild stress

Our previous study has found that zileuton, a selective 5-lipoxygenase (5LO) inhibitor, abrogated lipopolysaccharide-induced depressive-like behaviors and hippocampal neuroinflammation. Herein, we further extended our curiosity to investigate effects of zileuton on stress-induced depressive-like behaviors. Our data indicated that zileuton significantly ameliorated depressive-like behaviors in mice subjected to chronic mild stress (CMS), as shown in the tail suspension test, forced swimming test and novelty-suppressed feeding test. The further studies indicated that zileuton suppressed hippocampal neuroinflammation, evidenced by lower levels of TNF-α, IL-1β and nuclear NF-κB p65 as well as decreased number of Iba1-positive cells. It also significantly ameliorated hippocampal apoptosis, indicated by deceased number of TUNEL-positive cells, deceased ratio of cleaved caspase-3/procaspase-3 and increased ratio of Bcl-2/Bax. More importantly, zileuton increased the level of synaptic proteins PSD-95 and SYN and the number of NeuN⁺/BrdU⁺ cells in the hippocampus. Over all, zileuton alleviated CMS-induced depressive-like behaviors, neuroinflammatory and apoptotic responses, abnormalities of synapse and neurogenesis in the hippocampus, suggesting that it might has beneficial effects on depression.

Emerging Roles of 5-Lipoxygenase Phosphorylation in Inflammation and Cell Death

5-Lipoxygenase (ALOX5) is an iron-containing and nonheme dioxygenase that catalyzes the peroxidation of polyunsaturated fatty acids such as arachidonic acid. ALOX5 is the rate-limiting enzyme for the biosynthesis of leukotrienes, a family of proinflammatory lipid mediators derived from arachidonic acid. ALOX5 also make great contributions to mediating lipid peroxidation. In recent years, it has been discovered that ALOX5 plays a central role in cell death including apoptosis, pyroptosis, and ferroptosis, a newly discovered type of cell death. According to the previous studies, ALOX5 can regulate cell death in two ways: one is inflammation and the other is lipid peroxidation. Meanwhile, it has been shown that ALOX5 activity is regulated by several factors including protein phosphorylation, ALOX5-interactng protein, redox state, and metal ions such as iron and calcium. In this review, we aim to summarize the knowledge on the emerging roles of ALOX5 protein phosphorylation in the regulation of cell death and inflammation in order to explore a potential target for human diseases.

Resveratrol downregulates the TLR4 signaling pathway to reduce brain damage in a rat model of focal cerebral ischemia

Previous studies have demonstrated that inflammation and disruption of the blood-brain barrier (BBB) are important pathological processes during focal cerebral ischemia. Therefore, the present study evaluated the neuroprotective effects of resveratrol against brain damage, inflammation and BBB disruption in rats with focal cerebral ischemia and assessed the potential underlying molecular mechanisms. Sprague-Dawley rats underwent cerebral ischemia/reperfusion (IR) and then received intraperitoneal resveratrol (10 and 100 mg/kg) 2 h following the onset of ischemia. Following 24 h of ischemia, neurological deficit scores, cerebral infarctions, morphological characteristics, cerebral water content, myeloperoxidase (MPO) activity and Evans blue extravasation were assessed. Additionally, the protein expression levels of Toll-like receptor 4 (TLR4) and nuclear factor (NF)-κB p65 were detected using western blot analyses, the mRNA expression levels of cyclooxygenase-2 (COX-2) and matrix metalloproteinase-9 (MMP-9) were examined by reverse-transcription polymerase chain reaction, and tumor necrosis factor (TNF)-α and interleukin (IL)-1β blood levels were determined by ELISA. Resveratrol significantly reduced neurological deficit scores, cerebral infarct sizes, neuronal injury, MPO activity and EB content. Cerebral ischemia increased the expression levels of TLR4, NF-κB p65, COX-2, MMP-9, TNF-α and IL-1β, but all of these factors were reduced by resveratrol. In conclusion, the present data suggest that resveratrol reduces inflammation, BBB disruption and brain damage in rats following focal cerebral ischemia. Additionally, the neuroprotective effects of resveratrol against cerebral ischemia may be associated with downregulation of the TLR4 pathway.

A novel therapeutic potential of cysteinyl leukotrienes and their receptors modulation in the neurological complications associated with Alzheimer's disease

Cysteinyl leukotrienes (cysLTs) are member of eicosanoid inflammatory lipid mediators family produced by oxidation of arachidonic acid by action of the enzyme 5-lipoxygenase (5-LOX). 5-LOX is activated by enzyme 5-Lipoxygenase-activating protein (FLAP), which further lead to production of cysLTs i.e. leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4). CysLTs then produce their potent inflammatory actions by activating CysLT1 and CysLT2 receptors. Inhibitors of cysLTs are indicated in asthma, allergic rhinitis and other inflammatory disorders. Earlier studies have associated cysLTs and their receptors in several neurodegenerative disorders diseases like, multiple sclerosis, Parkinson's disease, Huntington's disease, epilepsy and Alzheimer's disease (AD). These inflammatory lipid mediators have previously shown effects on various aggravating factors of AD. However, not much data has been elucidated to test their role against AD clinically. Herein, through this review, we have provided the current and emerging information on the role of cysLTs and their receptors in various neurological complications responsible for the development of AD. In addition, literature evidences for the effect of cysLT inhibitors on distinct aspects of abnormalities in AD has also been reviewed. Promising advancement in understanding on the role of cysLTs on the various neuromodulatory processes and mechanisms may contribute to the development of newer and safer therapy for the treatment of AD in future.

Antidepressant-like effect of zileuton is accompanied by hippocampal neuroinflammation reduction and CREB/BDNF upregulation in lipopolysaccharide-challenged mice

BACKGROUND

Recent studies demonstrated beneficial effects of zileuton, a 5-lipoxygenase (5LO) inhibitor, on some brain diseases in animal models, but the role of zileuton in the depression remains unknown.

METHODS

We investigated the effects of zileuton on depressive behaviors using tail suspension test (TST), forced swimming test (FST) and novelty-suppressed feeding test (NSFT) in mice injected with lipopolysaccharide (LPS). The 5LO level, activation of microglia, NF-κB p65, TNF-α, IL-1β, brain-derived neurotrophic factor (BDNF), and c-AMP response element-binding protein (CREB) were determined in the mouse hippocampus.

RESULTS

We firstly found that the expression of hippocampal 5LO was gradually increased over LPS exposure and was reversed by fluoxetine administration. Zileuton significantly suppressed LPS-induced depressive behaviors, evidenced by the decreases in immobility time in TST and FST, as well as the latency to feed in NSFT. This treatment pronouncedly alleviated LPS-induced neuroinflammatory response, characterized by decreased 5LO, suppressed activation of microglia, decreased NF-κB p65, TNF-α and IL-1β, and significantly increased the ratio of p-CREB/CREB or mBDNF/proBDNF in the hippocampus of the LPS-challenged mice.

CONCLUSIONS

Zileuton abrogates LPS-induced depressive-like behaviors and neuroinflammation, and enhances CREB/BDNF signaling in the hippocampus, suggesting that zileuton could have potential therapeutic value for depression.

Effect of zileuton on osteoporotic bone and its healing, expression of bone, and brain genes in rats

Estrogen deficiency and aging are associated with osteoporosis, impaired bone healing, and lower cognitive performance. Close functional and physical connections occur between bone and the central nervous system. An anti-inflammatory drug, zileuton (which is an inhibitor of arachidonate 5-lipoxygenase), is known to have a positive effect on bone tissue repair and brain ischemia. We studied the effect of zileuton on osteopenic bone and its healing and on the genes considered to be crucial for the cross talks between bone and brain. Three-month-old Sprague-Dawley rats were ovariectomized or left untreated. After 8 wk, bilateral metaphyseal tibia osteotomy with plate osteosynthesis was performed in all rats. Ovariectomized rats were fed with food containing zileuton (1, 10, or 100 mg/kg body wt) for 5 wk. In tibiae, bone volume, callus and cortical volume, and gene expression of osteocalcin and alkaline phosphatase were enhanced by zileuton (10 or 100 mg); biomechanical properties and bone density were not changed. In femur, zileuton enlarged cortical volume distal and trabecular volume proximal, decreasing their density. The expression level of brain Sema3a, known to regulate bone mass positively, was downregulated after ovariectomy. In contrast, bone Sema4d, a negative regulator of bone mass, was upregulated in the tibia callus after ovariectomy, whereas zileuton treatment (10 or 100 mg) resulted in reverse effects. Here, we describe for the first time the expression of Rbbp4 mRNA and its increase in tibia after ovariectomy. Zileuton caused downregulation of Rbbp4 in the hippocampus and had an effect on bone healing, changed the expression of genes involved in cross talk between bones and brain, and may be a potent drug for further examination in estrogen deficiency-related dysfunction(s). NEW & NOTEWORTHY Zileuton, a 5-lipoxygenase inhibitor, increased bone volume, callus and cortical volume in osteotomized tibia, and trabecular and cortical volume in femur. Although the expression of Sema3a (positively regulating bone mass) in brain was downregulated and Sema4d (negatively regulating bone mass) was upregulated in tibia callus after ovariectomy, zileuton could counteract these effects. Rbbp4 (involved in age-related memory loss) was increased in tibia callus after ovariectomy.

Cysteinyl Leukotrienes as Potential Pharmacological Targets for Cerebral Diseases

Cysteinyl leukotrienes (CysLTs) are potent lipid mediators widely known for their actions in asthma and in allergic rhinitis. Accumulating data highlights their involvement in a broader range of inflammation-associated diseases such as cancer, atopic dermatitis, rheumatoid arthritis, and cardiovascular diseases. The reported elevated levels of CysLTs in acute and chronic brain lesions, the association between the genetic polymorphisms in the LTs biosynthesis pathways and the risk of cerebral pathological events, and the evidence from animal models link also CysLTs and brain diseases. This review will give an overview of how far research has gone into the evaluation of the role of CysLTs in the most prevalent neurodegenerative disorders (ischemia, Alzheimer's and Parkinson's diseases, multiple sclerosis/experimental autoimmune encephalomyelitis, and epilepsy) in order to understand the underlying mechanism by which they might be central in the disease progression.

Inhibition of 5-lipoxygenase by zileuton in a rat model of myocardial infarction

OBJECTIVE

The goal of the present study was to investigate the effects of 5-lipoxygenase (5-LOX) inhibition, alone and with cyclooxygenase (COX) inhibitors, on inflammatory parameters and apoptosis in ischemia/reperfusion (I/R)-induced myocardial damage in rats. For this purpose, zileuton, a selective and potent inhibitor of 5-LOX, resulting in suppression leukotriene production, was used.

METHODS

Male Wistar rats (200-250 g; n=12 per group) were used in the study. I/R was performed by occluding the left coronary artery for 30 minutes and 2 hours of reperfusion of the heart. Experimental groups were I/R group, sham I/R group, zileuton (5 mg/kg orally, twice daily)+I/R group, zileuton+indomethacin (5 mg/kg intraperitoneally)+I/R group, zileuton+ketorolac (10 mg/kg subcutaneously)+I/R group, and zileuton+nimesulide (5 mg/kg subcutaneously)+I/R group. Following I/R, blood samples were collected to measure tumor necrosis factor alpha (TNF-α), and left ventricles were excised for evaluation of microscopic damage; malondialdehyde (MDA), glutathione, nuclear factor (NF)-κB assays; and evaluation of apoptosis.

RESULTS

Left ventricle MDA in I/R group was higher compared to sham group; however, it did not show significant change with zileuton. Although tissue injury in I/R group was less severe in all treatment groups, it was not statistically significant. NF-κB H-score and apoptotic index, which were higher in I/R group compared to sham I/R, were decreased with application of zileuton (H-score: p<0.01; apoptotic index: p<0.001). Zileuton had no significant effect on increased serum TNF-α levels in I/R group.

CONCLUSION

5-LOX inhibition in rat myocardial infarction model attenuated increased left ventricle NF-κB expression and apoptosis and these actions were not modulated by COX inhibitors.

5-LOX Inhibitor Zileuton Reduces Inflammatory Reaction and Ischemic Brain Damage Through the Activation of PI3K/Akt Signaling Pathway

Previous studies from our laboratories showed that an anti-inflammatory drug, 5-lipoxygenase inhibitor zileuton, attenuates ischemic brain damage via inhibiting inflammatory reaction. However, it was elusive whether zileuton attenuates inflammatory reaction and ischemic brain damage through the modulation of PI3K/Akt signaling pathway. In the present study, we, for the first time, investigated whether PI3K/Akt pathway was involved in zileuton's anti-inflammatory and neuroprotective properties against brain damage following experimental ischemic stroke. Adult male Sprague-Dawley rats underwent middle cerebral artery occlusion (MCAO), then received treatment with zileuton or vehicle after the onset of ischemia. LY294002 was injected intracerebroventricularly to inhibit the activation of PI3K/Akt signaling pathway selectively. Neurological deficit scores, cerebral infarct volume, morphological characteristic and cerebral water content were assessed 24 h after cerebral ischemia. The enzymatic activity of myeloperoxidase (MPO) was measured 24 h after cerebral ischemia. Expression of p-Akt, t-Akt and COX-2 in ischemic brain were determined by western blot. NF-κB p65 immuno-positive cells in ischemic brain were detected 24 h after cerebral ischemia. The content of TNF-α in blood was examined by ELISA. 5-LOX inhibitor zileuton significantly reduces neurological deficit scores, cerebral infarct volume, cerebral water content, ischemic neuronal injury and the enzymatic activity of MPO, all of which were abolished by LY294002 administration. Zileuton significantly up-regulates the expression of p-Akt, which was inhibited by LY294002 administration. Zileuton significantly down-regulates the over-expression of NF-κB p65 and COX-2, and attenuates the release of TNF-α, all of which were disminished by LY294002 administration. These results suggest that zileuton attenuates ischemic brain damage by inhibiting inflammatory reaction through the activation of PI3K/Akt signaling pathway.

The 5-Lipoxygenase Inhibitor Zileuton Confers Neuroprotection against Glutamate Oxidative Damage by Inhibiting Ferroptosis

5-Lipoxygenase (5-LOX) inhibitors have been shown to be protective in several neurodegenerative disease models; however, the underlying mechanisms remain unclear. We investigated whether 5-LOX inhibitor zileuton conferred direct neuroprotection against glutamate oxidative toxicity by inhibiting ferroptosis, a newly identified iron-dependent programmed cell death. Treatment of HT22 mouse neuronal cell line with glutamate resulted in significant cell death, which was inhibited by zileuton in a dose-dependent manner. Consistently, zileuton decreased glutamate-induced production of reactive oxygen species but did not restore glutamate-induced depletion of glutathione. Moreover, the pan-caspase inhibitor Z-Val-Ala-Asp(OMe)-fluoromethyl ketone (ZVAD-fmk) neither prevented HT22 cell death induced by glutamate nor affected zileuton protection against glutamate oxidative toxicity, suggesting that zileuton did not confer neuroprotection by inhibiting caspase-dependent apoptosis. Interestingly, glutamate-induced HT22 cell death was significantly inhibited by the ferroptosis inhibitor ferrostatin-1. Moreover, zileuton protected HT22 neuronal cells from erastin-induced ferroptosis. However, we did not observe synergic protective effects of zileuton and ferrostatin-1 on glutamate-induced cell death. These results suggested that both the 5-LOX inhibitor zileuton and the ferropotosis inhibitor ferrostatin-1 acted through the same cascade to protect against glutamate oxidative toxicity. In conclusion, our results suggested that zileuton protected neurons from glutamate-induced oxidative stress at least in part by inhibiting ferroptosis.

Regulation of gamma-secretase activating protein by the 5Lipoxygenase: in vitro and in vivo evidence

The formation of Aβ is directly controlled by the γ-secretase complex and its activator, γ-secretase activating protein (GSAP). GSAP derives from a C-terminal fragment of a larger precursor protein via a caspase-3 mediated cleavage. However, the mechanism regulating this process remains unknown. Here we provide in vitro experimental evidence that 5-Lipoxygenase (5LO) is as an endogenous regulator for GSAP formation, but not for other known γ-secretase modulators, by directly and specifically activating caspase-3. These results were confirmed in vivo by using transgenic mouse models of Alzheimer’s disease in which 5LO level and activity were modulated genetically or pharmacologically. Taken together, our findings demonstrate that GSAP cleavage via caspase-3 is regulated and depend upon the availability of 5LO further establishing this protein as an attractive and viable therapeutic target for Alzheimer’s disease.

The protective effect of caffeic acid on global cerebral ischemia-reperfusion injury in rats

Ischemic stroke is a major cause of death and disability all over the world. Ischemic stroke results from a temporary or permanent reduction of cerebral blood flow that leads to functional and structural damage in different brain regions. Despite decades of intense research, the beneficial treatment of stroke remains limited. In light of this, the search for effective means ameliorating cerebral ischemia-reperfusion injury (CIRI) is one of the major problems of experimental medicine and biology. Recently, the 5-Lipoxygenase (5-LO, a key enzyme metabolizing arachidonic acid to produce leukotrienes) inhibitors have been showed to protect brain against ischemic damage in animal model of cerebral ischemia. Caffeic acid, an inhibitor of 5-LO, is a phenolic compound widely distributed in medicinal plants. The aim of this study was to investigate the effect of caffeic acid on global cerebral ischemia-reperfusion injury in rats. The study was carried out on 45 rats that were randomly divided into five groups: the sham group (n = 9), I/R non-treated group (n = 9), I/R-caffeic acid group (10 mg · kg⁻¹) (n = 9), I/R-caffeic acid group (30 mg · kg⁻¹) (n = 9) and I/R-caffeic acid group (50 mg · kg⁻¹) (n = 9). Global cerebral ischemia was induced by bilateral carotid artery occlusion for 20 min followed by reperfusion. Spatial learning and memory was evaluated using Morris water maze. Histopathological changes of hippocampus neurons was observed using HE staining. Superoxide dismutase (SOD, the antioxidant enzyme) activities and malondialdehyde (MDA, an oxidative stress biomarker) contents were detected. NF-κBp65 expression was detected by the methods of immunohistochemistry. Caffeic acid markedly reduced the escape latency, relieved hippocampal neurons injury and increased neuron count compared with those of I/R non-treated rat. NF-κBp65 expression and MDA content decreased significantly, and SOD activities increased significantly in hippocampus. Compared with sham group, 5-LO expression increase significantly in I/R non-treated group rat, and caffeic acid markedly reduced 5-LO expression. The results of the study suggest that caffeic acid has a significant protective effect on global cerebral ischemia-reperfusion injury in rats. The neuroprotective effects is likely to be mediated through the inhibition of 5-LO.

Montelukast, a cysteinyl leukotriene receptor-1 antagonist protects against hippocampal injury induced by transient global cerebral ischemia and reperfusion in rats

Cysteinyl leukotrienes (CysLTs) are potent pro-inflammatory and immune modulating lipid mediators involved in inflammatory diseases and were boosted in human brain after acute phase of cerebral ischemia. The antagonism of CysLTs receptors may offer protection against ischemic damage. Therefore it seemed interesting to study the possible neuroprotective effect of Montelukast, a CysLTR1 antagonist in global cerebral ischemia/reperfusion (IR) injury in rats. Global cerebral ischemia-reperfusion was induced by bilateral carotid artery occlusion for 15 min followed by 60 min reperfusion period. Animals were randomly allocated into three groups (n = 30 per group): Sham operated, I/R control and rats treated with montelukast (0.5 mg/kg, po) daily for 7 days then I/R was induced 1 h after the last dose of montelukast. After reperfusion rats were killed by decapitation, brains were removed and both hippocampi separated and the following biochemical parameters were estimated; lactate dehydrogenase activity, oxidative stress markers (lipid peroxides, nitric oxide and reduced glutathione), inflammatory markers (myeloperoxidase, tumor necrosis factor-alpha, nuclear factor kappa-B, interleukin-6 and interleukin-10), apoptotic biomarkers (caspase 3 and cytochrome C), neurotransmitters (glutamate, gamma aminobutyric acid), Cys-LTs contents and CysLT1 receptor expression; as well as total brain infarct size and histopathological examination of the hippocampus were assessed. Montelukast protected hippocampal tissue by reducing oxidative stress, inflammatory and apoptotic markers. Furthermore, it reduced glutamate and lactate dehydrogenase activity as well as infarct size elevated by I/R. These results were consistent with the histopathological findings. Montelukast showed a neuroprotective effects through antioxidant, anti-inflammatory and antiapoptotic mechanisms.

Repetitive ischemic preconditioning attenuates inflammatory reaction and brain damage after focal cerebral ischemia in rats: involvement of PI3K/Akt and ERK1/2 signaling pathway

Ischemic preconditioning (IPC) has been demonstrated to provide a neuroprotection against brain damage produced by focal cerebral ischemia. However, it is elusive whether ischemic preconditioning attenuates ischemic brain damage through modulating phosphatidylinositol 3-kinase/Akt (PI3K/Akt) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. In the present study, we first explored the best scheme of repetitive ischemic preconditioning (RIPC) to protect rat brain against ischemic damage and then further investigated the underlying mechanisms in RIPC's neuroprotection. Adult male Sprague-Dawley rats underwent ischemic preconditioning or (and) middle cerebral artery occlusion (MCAO). LY294002 or (and) PD98059 were injected intracerebroventricularly to selectively inhibit the activation of PI3K/Akt or ERK1/2. Neurological deficit scores, cerebral infarct volume, and morphological characteristic were detected at corresponding time after cerebral ischemia. The enzymatic activity of myeloperoxidase (MPO) was measured 24 h after cerebral ischemia. Expressions of p-Akt, t-Akt, p-ERK1/2, t-ERK1/2, nuclear factor-kappa B (NF-κB) p65, and cyclooxygenase-2 (COX-2) in ischemic brain were determined by Western blot. The release of tumor necrosis factor-α (TNF-α) in blood was examined by ELISA. In the various schemes of RIPC, IPC2 × 5 min causes less neuronal damage in the cortex and subcortex of ischemic brain and provides an obvious alleviation of cerebral infarction and neurological deficit after lethal ischemia. IPC2 × 5 min significantly reduces cerebral infarct volume, neurological deficit scores, and MPO activity; all of which were diminished by LY294002 or (and) PD98059. IPC2 × 5 min significantly upregulates the expressions of p-Akt and p-ERK1/2, which were inhibited by LY294002 or (and) PD98059. IPC2 × 5 min significantly downregulates the expressions of NF-κB p65 and COX-2 and attenuates the release of TNF-α; all of which were abolished by LY294002 or (and) PD98059. IPC2 × 5 min is the best scheme of RIPC to protect rat brain against cerebral ischemia. IPC2 × 5 min attenuates brain damage in rats subjected to lethal ischemia, and this neuroprotection is associated with inhibition of neuroinflammation through modulating PI3K/Akt and ERK1/2 signaling pathway.